Lupinus tidestromii is an endangered plant that grows on coastal sand dunes in California and is consumed by native rodent seed predators. L. tidestromii experiences high rates of fruit and seed predation. Using field experiments, we determined the amount of predation and we determined in which locations plants experience highest levels of predation. To determine the effect of predation of population growth rates, we created a stochastic matrix projection model.
Results/Conclusions

Our observational and experimental data shows that the high predation results from apparent competition with the invasive beachgrass Ammophila arenaria. The model projects population growth rate in the presence and absence of predation. Populations are projected to decline towards extinction if current levels of predation continue. Removal of the invasive A. ammophila may result in increased growth rates of L. tidestromii. Although many population viability analyses have shown the effects of predation and herbivory on plant populations, this is the first to quantify the indirect effect of an invasive species on the viability of an endangered species.